The objective is to study the biology of tissue transplantation. The methods will be primarily the observation and possible manipulation of the homograft reaction in genetically defined strains of rodents. Attention will be directed especially to the understanding of why certain homografted tissues (kidney, ovary, blood vessels) may be rejected less vigorously than others (skin). Attempts will also be made to define certain conditions under which even skin homografts may be accepted - e.g. alterations in lymphatic circulation to create immunologically privileged sites.